Galactic star formation takes place in cold, magnetized, molecular clouds which are dynamically dominated by supersonic turbulence. Using large-scale numerical simulations, our group is studying the structure and evolution of these turbulent molecular clouds.
Our evolutionary models have shown that turbulence dissipates rapidly, so that turbulence incorporated in a cloud from its formation stages cannot support it against self-gravitational collapse. In our models, this collapse commences in dense regions representing only a few percent of the mass of a cloud, potentially explaining the low efficiency of star formation. Our evolutionary models support the notion that GMCs must form and disperse rapidly; energetic feedback from massive star formation is likely responsible for this dispersal.
Our analysis of structure has shown that much of the moderate-density condensations observed in molecular tracers (e.g. 13CO) may be formed by Reynolds and Maxwell stresses at multiple spatial scales in the turbulent flow -- and may be highly transient. Using our simulated data cubes, we have developed and/or calibrated several methods to infer basic cloud properties from observables, including using linewidth/size distributions to determine the intrinsic velocity power spectrum, and using the dispersion in polarized-extinction angles to determine the mean magnetic field strength.
Evolution of column density (left) and a passive tracer to illustrate
turbulent diffusion (right) in a simulated
magnetically-supercritical molecular cloud
Column density and polarization in a simulated molecular cloud
Three-dimensional visualization of density structure in a turbulent cloud
Collaborators: Charles Gammie (U. Illinois) and Jim Stone (Princeton U.)
For more information, see our publications and Jim Stone's molecular cloud turbulence web page
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